1. Field of the Invention
The present invention relates to a method for producing a screw-top bottle-can having a screw-thread on which a cap is screwed, and a screw-top bottle-can.
Priority is claimed on Japanese Patent Application No. 2011-069474, filed Mar. 28, 2011, the content of which is incorporated herein by reference.
2. Background Art
As a container in which contents such as a beverage or the like is filled, a can (a bottle-can) which is made by aluminum alloy, with a mouth part having a male thread on which a cap is screwed, and has a bottle-shape, is known.
As disclosed by Patent Document 1 or Patent Document 2, the bottle-can is produced by forming a sheet metal of aluminum-alloy into a closed-end cylindrical body in which a bottom plate part and a cylindrical-side-surface part are united by drawing and ironing (DI process), making a shoulder part by reducing a diameter of an opening part and making an expanded cylindrical part at an upper part than the shoulder part for forming a thread, then performing a thread-forming process on the cylindrical part, performing a curl-forming process on an opening-end part, and the like.
In bottle-cans of this kind, inner and outer surfaces of the closed-end cylindrical body are coated before the process of reducing the diameter of the opening part. For processing the opening part particularly without damaging the coating of the inner surface, there is a method described in Patent Document 3.
Patent Document 3 describes an intermediate formed product before a thread-forming process in which a cylindrical part having an outer diameter of a middle of a major diameter and a minor diameter of a screw-thread is formed at a second-step section from an opening end by forming the mouth part so as to have at least two steps from shoulder part by drawing, and then the thread-forming process is performed with clamping the cylindrical part between an inner die and an outer die.